As part of my LAN Before Time rack project, I’m setting up classic PCs with a VGA and PS/2 KVM to manage them. However, one of my systems—a 486—lacks a PS/2 port for the mouse. A simple PS/2-to-serial adapter wasn’t enough; it required a proper signal conversion to work.
After some searching, I found this adapter kit on eBay: PS/2 to Serial Mouse Adapter. It’s based on an open-source project: necroware/ps2-serial-mouse-adapter. The kit didn’t include instructions, and the project assumes you already know how to assemble it; I decided to document my build process step by step.
A Quick Note on KVM Compatibility
This adapter worked flawlessly when I plugged a PS/2 HP Laser Mouse directly into the 486. However, when connected through my KVM, it worked for a few seconds before stopping. After some digging, I found a pull request from last year that mentioned a KVM fix. Flashing that updated firmware completely resolved my issue! Unfortunately, the main repository hasn’t been updated in two years, so hopefully, it gets some attention.
What’s Next?
Below, I’ll walk through assembling the adapter. After that, I’ll cover how to flash the updated firmware using a USB-to-TTL converter. These converters are cheap and easy to find—here’s the one I used: USB to TTL Adapter. Finally, I will show a case I designed and 3D printed for the device.
Steps

- Put the serial connector through the top side of the board and solder it in place on the bottom, starting with the mounting legs and using plenty of solder. These take a lot of the strain of the connections. Then carefully do each of the data pins, making sure not to bridge any.

- Insert the lower chip socket, and solder in place on the underside.

- The Arduino Pro has 3 different parts we need to solder. The first is the head with the 90 degree pins at the end. This will allow us later to flash the controller if we want to move to other firmware. Put those through the top (the side with the chip) and then solder them in the underside.
- Next, put the Arduino header pins in the bottom. I put them into the header connector to hold them in place. Do not put too much heat on each pin with the plastic part below. (Not my best soldering job)

- Solder in the 10k resister, here I am soldering it on the bottom while it went in through the top. After it is in, cut of the excess legs.

- Solder in the PS/2 port, use a good amount of solder on the mounting points so it doesn’t move when inserted, then solder the data pins.

- Solder in the micro-usb port, careful of the tiny pins.

- Add the jumper pins, solder them in.
- Now time for the capacitors, these are polarized, note the right side of the silk screen is white that should line up with the white side of the cap. (the shorter leg side)

- Finish up by soldering all the pin headers for the controller to sit on the board.



The board should now be complete! If you bought it from the seller I did, (who has been great, and I have bought other items from) then you have the main repos firmware on it. I won’t go too far in depth for this, but if you clone the fork down you can then use Platform.IO to flash the firmware. There are guides out there to do this on. Platform.IO is great when doing Arduino projects.
If you go the same kit I did, then it comes with a “pro16MHzatmega168” not the “pro16MHzatmega328” used in the Pull Request. Change the two lines where the 328 is mentioned to the 168-model string. If you do not, you will get a “timeout connecting to Arduino” when attempting to flash.
As mentioned, you need a TTL converter, then to flash the chip. The TTL converter (which I hadn’t used before) pins actually line up with the pins on the Arduino Pro. You need to hold it there for a total of 30 seconds while it flashes. You can just stick the header pins of the Arduino through the holes of the converter, then hit send via Platform.IO.

3D Printed Case
This is a device I will keep behind my old PC, and I didn’t want it to be a raw circuit board. I didn’t see any cases to 3D print, so I put one together. This was the first time I made a case that used little feet to snap the top and bottom half together; no screws! I also put little towers in to hold down the PCB in place. It took a few revisions, but I think came out nicely. There is also a little window to hit the reset button if needed. The black case was the second revision, the white case is the first.
Model: https://thangs.com/mythangs/file/1301661















































